Hydraulic energy accumulator

ABSTRACT

Example energy storage systems ( 20, 20′, 20 ″) comprises a fluid circuit ( 22, 22′, 22 ″) and an electrical unit ( 24, 24′, 24 ″) configured to operate as a motor in a first phase of operation and to operate as a generator in a second phase of operation. The fluid circuit ( 22, 22′, 22 ″) comprises a first fluid container ( 30, 30′, 30 ″) situated so content of the first fluid container experiences a first pressure level; a tank ( 32, 32′, 32 ″) having its content at a second pressure level (the second pressure level being less than the first pressure level): and, a first hydraulic motor/pump unit ( 34, 134, 34 ″) connected to communicate a first working fluid between the tank and the first fluid container. In the first phase of operation electricity is supplied to the first hydraulic/motor unit ( 34, 134, 34 ″) whereby the first hydraulic/motor unit transmits the first working fluid from the tank into the first fluid container ( 30, 30′, 30 ″). In the second phase of operation pressurized first working fluid in the first fluid container ( 30, 30′, 30 ″) is transmitted from the first fluid container through the first hydraulic/motor unit  34, 134, 34 ″) to the tank ( 32, 32′, 32 ″), thereby causing the electrical unit ( 24, 24′, 24 ″) to generate electricity.

This application is a continuation of U.S. Non-provisional patentapplication Ser. No. 11/947,238, filed Nov. 29, 2007, which claims thepriority and benefit of U.S. Provisional Patent Application 60/867,658,filed Nov. 29, 2006, entitled “Hydraulic Energy Accumulator”, both ofwhich are incorporated herein by reference in their entirety.

BACKGROUND

I. Technical Field

This invention pertains to the storage of energy, and particularly tothe storage of electricity during a low demand time period for retrievalduring a high demand time period.

II. Related Art and Other Considerations

In many geographical or utility service areas the demand for electricityvaries during a day or other time period. For example, power consumptionduring a hot summer day may be considerably greater than for the night.And typically the per unit cost of power is greater during a peak timeperiod than for an off-peak or lower demand time period, with a kilowatthour (KWH) sometimes being many times more expensive in peak demand timeperiods than in low demand periods.

Supply, delivery, and affordability of power during peak times can thusbe problematic. For this reason in some localities or regions it can beadvantageous to accumulate and store power (e.g., electricity) duringnon-peak time periods so that the stored power can instead be utilizedduring a peak demand time. In view of such factors as scarcity and/orthe greater cost of electricity during peak demand times, theaccumulation and storage of electricity for time re-distribution isoften desirable, even though the act of accumulating and storing theelectricity may itself consume energy.

Electrical power availability can be time re-distributed in severaltraditional ways. One way is to store electrical energy by pumping waterto a high altitude during non-peak demand times and then turbining thewater at peak hours for electricity generation. Other ways involve suchtechniques or mechanisms such as compressing air in caves (CAES) duringnon-peak demand times; use of flywheels, and chemical storage or thelike. Example prior art techniques are non-exhaustively illustrated inU.S. Pat. No. 4,281,256; U.S. Pat. No. 3,163,985; and U.S. Pat. No.4,353,214, for example.

Without electricity re-distribution techniques such as the foregoing,industry is forced to increase production capacity in order to meet everincreasing peak demands. And yet some of the existing electricityre-distribution techniques have their own disadvantages andinefficiencies.

BRIEF SUMMARY

An example energy storage system comprises a fluid circuit comprising anelectrical unit configured to operate as a motor in a first phase ofoperation and to operate as a generator in a second phase of operation.The fluid circuit comprises a first fluid container situated so contentof the first fluid container experiences a first pressure level; a tankhaving its content at a second pressure level (the second pressure levelbeing less than the first pressure level): and, a first hydraulicmotor/pump unit connected to communicate a first working fluid betweenthe tank and the first fluid container. In the first phase of operationelectricity is supplied to the first hydraulic/motor unit whereby thefirst hydraulic/motor unit transmits the first working fluid from thetank into the first fluid container. In the second phase of operationpressurized first working fluid in the first fluid container istransmitted from the first fluid container through the firsthydraulic/motor unit to the tank, thereby causing the electrical unit togenerate electricity.

In some example embodiments, the first hydraulic motor/pump unit isconnected between the tank and the first fluid container; the firstfluid container is situated below a reference pressure level; and thefirst fluid container is submerged. Pressure experienced by the firstfluid container at the first pressure level occurs by reason ofsubmersion and causes, during the second phase of operation, the firstworking fluid to be forced back to the tank. Transmission of the firstworking fluid back to the tank causes the first hydraulic motor/pumpunit to operate as a motor to drive the electrical unit which operatesas a generator of electricity.

In some example embodiments, the first fluid container comprises a firstflexible bladder which is submerged in liquid (e.g., under a referencepressure level such as a surface level of the liquid, e.g., sea level).In some example embodiments, the fluid circuit and the electrical unitare also situated below the reference pressure level (e.g., below sealevel). In such example embodiments, the system can further comprise aballast configured to prevent at least a portion of the system fromfloating.

Another example embodiment of energy storage system further comprises asecond fluid container; a second hydraulic motor/pump unit; and, a thirdhydraulic motor/pump unit. The second fluid container is situated sothat content of the second fluid container is at a second containerpressure level, the second container pressure level being less than thefirst pressure level. The second hydraulic motor/pump unit isoperatively connected to the electrical unit and fluidically connectedbetween the second fluid container and the third hydraulic motor/pumpunit. The third hydraulic motor/pump unit is fluidically connectedbetween the second hydraulic motor/pump unit and the first fluidcontainer. The second hydraulic motor/pump unit and the third hydraulicmotor/pump unit are configured during the first phase of operation tooperate as pumps to transmit fluid from the second fluid container tothe first fluid container. The second hydraulic motor/pump unit and thethird hydraulic motor/pump unit are configured during the second phaseof operation to operate as motors as fluid from the first fluidcontainer is transmitted to the second fluid container. The electricalunit is configured during the first phase of operation to operate as themotor for the second hydraulic motor/pump unit and during the secondphase of operation to operate as a generator driven by the secondhydraulic motor/pump unit.

Another example embodiment of energy storage system further comprises asecond fluid container, with the first hydraulic motor/pump unit beingfluidically connected between the tank and the second fluid containerfor communicating a second working fluid between the tank and the secondfluid container. In this example embodiment, the first working fluidcomprises compressed gas. The first fluid container is submerged in aliquid and has a fluid container first internal region in communicationwith the liquid and a fluid container second internal region incommunication with the compressed gas.

The first hydraulic motor/pump unit is configured during the first phaseof operation to operate as a pump to transmit the second working fluidfrom the second fluid container to the tank and thereby drive the firstworking fluid from the tank to the fluid container first internal regionand during the second phase of operation to operate as a motor as thesecond working fluid is driven by the first working fluid from the tankto the second fluid container. The electrical unit is configured duringthe first phase of operation to operate as the motor for the firsthydraulic motor/pump unit and during the second phase of operation tooperate as a generator driven by the first hydraulic motor/pump unit.

One or more of the example embodiments typically additionally comprisesan electrical power source and a cable network configured during thefirst phase of operation to convey electricity from the electrical powersource to the electrical unit to operate the electrical unit during thefirst phase of operation and configured during the second phase ofoperation to transmit electricity generated by the electrical unit tothe electrical power source. In differing embodiments, the electricalpower source can be a power grid; a storage cell; and/or a renewablepower source. As an example implementation, a transformer may beconnected on the cable network between the electrical power source andthe electrical unit.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features, and advantages of theinvention will be apparent from the following more particulardescription of preferred embodiments as illustrated in the accompanyingdrawings in which reference characters refer to the same partsthroughout the various views. The drawings are not necessarily to scale,emphasis instead being placed upon illustrating the principles of theinvention.

FIG. 1 is a schematic view of an energy storage system according to anexample embodiment including a fluid circuit and an electrical unit.

FIG. 1A is a schematic view showing operation of the energy storagesystem of FIG. 1 in a first phase of operation.

FIG. 1B is a schematic view showing operation of the energy storagesystem of FIG. 1 in a second phase of operation.

FIG. 2 is a schematic view of the energy storage system of FIG. 1employed in a submerged implementation.

FIG. 3 is a schematic view of an energy storage system according to anexample embodiment and further showing an example power station servedby the energy storage system.

FIG. 4 is a schematic view of an energy storage system connected to apower supply system which is in the form of an electrical grid.

FIG. 5 is a schematic view of an energy storage system connected to apower supply system which is in the form of natural energy source suchas a wind-driven power source.

FIG. 6 is a schematic view of an energy storage system according toanother example embodiment.

FIG. 7 is a schematic view of an energy storage system according to yetanother example embodiment.

FIG. 8 is a schematic view of an energy storage system according tostill yet another example embodiment.

DETAILED DESCRIPTION

In the following description, for purposes of explanation and notlimitation, specific details are set forth such as particulararchitectures, interfaces, techniques, etc. in order to provide athorough understanding of the present invention. However, it will beapparent to those skilled in the art that the present invention may bepracticed in other embodiments that depart from these specific details.That is, those skilled in the art will be able to devise variousarrangements which, although not explicitly described or shown herein,embody the principles of the invention and are included within itsspirit and scope. In some instances, detailed descriptions of well-knowndevices, circuits, and methods are omitted so as not to obscure thedescription of the present invention with unnecessary detail. Allstatements herein reciting principles, aspects, and embodiments of theinvention, as well as specific examples thereof, are intended toencompass both structural and functional equivalents thereof.Additionally, it is intended that such equivalents include bothcurrently known equivalents as well as equivalents developed in thefuture, i.e., any elements developed that perform the same function,regardless of structure. Thus, for example, it will be appreciated bythose skilled in the art that block diagrams herein can representconceptual views of illustrative circuitry embodying the principles ofthe technology.

FIG. 1 illustrates a first example embodiment of an energy storagesystem 20 which includes fluid circuit 22 and electrical unit 24. Asexplained herein, electrical unit 24 is connected to operate as a motorin a first phase of operation (e.g., to generate a torque through arotatable shaft 26) and to operate as a generator in a second phase ofoperation (e.g., to generate an electrical current in response torotation of shaft 26). Fluid circuit 22 comprises fluid container 30;tank 32; and hydraulic motor/pump unit (HM/PU) 34. In an exampleimplementation of the first embodiment, fluid circuit 22 and electricalunit 24 are situated below a pressure reference level P_(R), e.g., belowsea level (meaning that fluid circuit 22 and electrical unit 24 aresubmerged in water or other liquid) or below ground level. “Submerged inliquid” or “submerged in water” can include, for example, submerged in anatural body of water such as the ocean or very deep lake, or submergedin a flooded mine, for example. Fluid container 30 is situated so thatits content is pressurized at a first pressure level, e.g., athydrostatic pressure P₁. For example, fluid container 30 can comprise afirst flexible bladder. The content of tank 32 is at a second pressurelevel P₂ (e.g., vacuum). Thus, P₂<P₁ since, e.g., rigid walls of tank 32isolate or insulate the content of tank 32 from any forces actingoutside tank 32 and maintain vacuum within tank 32.

In fluid circuit 22 hydraulic motor/pump unit (HM/PU) 34 is connected tocommunicate a first working fluid between tank 32 and fluid container30. For example, and as illustrated in FIG. 1, hydraulic motor/pump unit(HM/PU) 34 can be connected between tank 32 and fluid container 30 byappropriate fluidic tubes or pipes. For example, tank 32 is connected tohydraulic motor/pump unit (HM/PU) 34 through fluid tube 36 and hydraulicmotor/pump unit (HM/PU) 34 is connected to fluid container 30 throughfluid tube 38.

The electrical unit 24 is connected by cable network 40 to power station42. In an example embodiment, power station 42 can comprise power supplysystem 44 and an optional power station controller 46. Electrical unit24 is configured to supply a torque via rotation of shaft 26 tohydraulic motor/pump unit (HM/PU) 34 during a first phase of operationso that the hydraulic motor/pump unit (HM/PU) 34 operates as a pump andtransmits a working fluid from tank 32 into fluid container 30. FIG. 1Ashows the first phase of operation, and particularly shows by arrow 50the power supply system 44 supplying electrical power to electrical unit24. As depicted by arrow 52, the power received by electrical unit 24during the first phase is used by electrical unit 24 to operate (viashaft 26) hydraulic motor/pump unit (HM/PU) 34 in a direction so thatthe working fluid stored in tank 32 is pumped through tubes 36 and 38and into fluid container 30 in the manner depicted by arrow 54. In theimplementation in which fluid container 30 comprises a first flexiblebladder, the working fluid pumped into fluid container 30 causes theflexible bladder of fluid container 30 to volumetrically expand againsthydrostatic pressure forces (pressure level P₁). Upon completion of thepumping of the first phase, fluid circuit 22 including hydraulicmotor/pump unit (HM/PU) 34 is sealed or shut so that the working fluiddoes not escape from fluid container 30 back into tank 32. The sealingor shutting of the fluid circuit and thus the sealing of the workingfluid in this manner may be accomplished by appropriate valves, e.g.,either valves internal to hydraulic motor/pump unit (HM/PU) 34 or valvespositioned downstream from hydraulic motor/pump unit (HM/PU) 34 (e.g.,in tube 38 or at a mouth of fluid container 30). Such valve(s) can becontrolled by a suitable controller such as controller 46. Thus, thecontroller can comprise electrical unit 24 or be situated at powerstation 42.

Electrical unit 24 is configured and controlled to generate electricityduring the second phase of operation. FIG. 1B shows the second phase ofoperation, wherein fluid circuit 22 is open so that pressurized workingfluid in fluid container 30 is transmitted from fluid container 30through pipes 38 and 36 and through pump 34 in the manner depicted byarrow to tank 32. In other words, with fluid circuit 22 open, workingfluid in fluid container 30 which is under hydrostatic pressure P₁escapes through fluid circuit 22 to tank 32 where pressure P₂(vacuum)<pressure P₁. In the second phase of operation, hydraulicmotor/pump unit (HM/PU) 34 is operated in reverse, e.g., as a motor toturn shaft 26, so that the working fluid flowing therethrough turns anarmature or the like at the end of shaft 26 so that electrical unit 24generates electricity. The electricity generated by electrical unit 24during the second phase of operation is applied on cable network 40 topower station 42 as depicted by arrow 64 in FIG. 1B.

In an example implementation illustrated in FIG. 2 wherein the energystorage system is submerged below sea level (SL), the system optionallycomprises a ballast 70 configured to prevent the system from floating.The power station 42 is situated on land 72, or even partially on afloating platform. Preferably the power station 42 is situated above thepressure reference level P_(R). In the example embodiment, cable network40 conveys electricity from electrical power source 44 to electricalunit 24 for use of the electricity to operate electrical unit 24 duringthe first phase of operation.

As shown in the foregoing example, non-limiting embodiments, one “cell”comprises storage tank 32; an electrical motor/generator in the form ofelectrical unit 24 which is coupled to hydraulic motor/pump unit (HM/PU)34; fluid container 30 (in the example form of a flexible (e.g., rubber)bladder); and switching means (e.g., valves) for the working fluid.

The FIG. 1 and FIG. 2 embodiment thus takes advantage of the pressureexistent at great depth in water. The pressure tank 32 filled withworking fluid and placed at great depth can be emptied with hydraulicmotor/pump unit (HM/PU) 34 (during the first operational phase oraccumulation period). For the second operational phrase or generationperiod, working fluid released back through hydraulic motor/pump unit(HM/PU) 34 causes electrical unit 24 to function as an electricalgenerator to generate electricity. As an example, at a depth of 2000meters, one MWH can be stored in a tank of 14 m diameter.

This submerged embodiment offers better efficiency than, for instance,CAES technology, since in CAES air heats up when compressed(cooling/heating it leads to energy loss). Moreover, the submergedembodiment of FIG. 1 and FIG. 2 can also be located in many placesaround continental coasts, and thus does not suffer from geographicallimitations such as those involved with CAES technology.

FIG. 3 shows an example implementation wherein transformer 76 isconnected between electrical unit 24 and power station 42. Preferablytransformer 76 is positioned at a relatively short distance fromelectrical unit 24, with a primary of transformer 76 being connected toelectrical unit 24 and a secondary of transformer 76 being connected topower station 42. Thus, as understood from the FIG. 3 implementationwhich includes transformer 76, cable network 40 carries a stepped downpower level from electrical unit 24 to power station 42. The transformer76 is thus preferably submerged, and has adequate casement to preventcontact of transformer 76 with liquid. For example, transformer 76 canbe provided in a same casement or liquid-tight housing as is electricalunit 24.

In one example implementation illustrated in FIG. 4, the electricalpower source (e.g., power supply system) of power station 42 is a powergrid 82. In another example implementation illustrated in FIG. 5, theelectrical power source of power station 42 is a natural or renewablepower source 84 such as a wind-driven or solar power source. Thus,energy storage system 20 can be used not only for storing electricityfrom power grid 82, but also from “wind farms” or solar cells or thelike floating directly above, creating a good match for remote islands,for instance.

In the FIG. 1 representation, the structure shown below the referencepressure constitutes a “cell”. Plural cells, such as the one shown inFIG. 1 or other figures hereof, can be connected to power supply system44 (whatever its type) on the shore or on land 72.

It should be appreciated that, in any of the foregoing or otherembodiments described herein, at least portions of the power station 42can be situated below the reference pressure level, e.g., below sealevel. For example, as illustrated in FIG. 6, transformer and switchingelements 90 can be located below the reference level or even compriseelectrical unit 24. In fact, in some implementations the electrical unit24 can have on one of its ends a motor/generator and on the other end ahigh voltage cable. In such implementation, the electrical unit 24 canhold electrical switches, a high voltage transformer, radiocommunication means, and so on. If submersed, the electrical unit 24should be protected from water by a separation tank or other suitablestructure (which may also include the motor/generator).

In a first phase or accumulation sequence of operation, the exampleembodiment of FIG. 6, the electrical energy is transported from surfacethrough cable 40 and transformer/switching portions 90, reachingelectrical unit 24 working as a motor. Through shaft 26 which connectselectrical unit 24 and hydraulic motor/pump unit (HM/PU) 34, themechanical energy activates the hydraulic motor/pump 34 that works as apump. The pumping action performed by hydraulic motor/pump unit (HM/PU)34 draws or even empties the working fluid from tank 32, therebycreating a vacuum in tank 32. The pumping action of hydraulic motor/pumpunit (HM/PU) 34 pushes the working fluid into fluid container 30, which(particularly when in the form of a flexible bladder) finds itself underhydrostatic pressure. In this way the electrical energy is convertedinto mechanical energy and finally into potential energy proportionalwith the volume of the hydraulic fluid and the pressure differencebetween the tank 32 (vacuumed) and the fluid container 30. The fluidcontainer 30 can be at a significant depth pressure, e.g., 100+ bar.

In a second phase of operation (also known as a recuperation/generationsequence), the potential energy is converted back into electricalenergy. The hydraulic working fluid from fluid container 30 (under highpressure) activates the hydraulic motor pump 34 (now acting as a motor)and escapes into tank 32 (under no pressure). The mechanical energy goesback through shaft 26 to the electrical unit 24 (now acting as agenerator). The electrical energy produced by electrical unit 24 goes tothe switch 24 of power station portions 90, though cable 40, and back tothe power grid.

The efficiency of a method such as that described above with referenceto FIG. 6, for example, is improved in contrast to a CAES-type system,since the present method has no change in working fluid volume. Thehydraulic working fluid used is incompressible compared with air used byCAES. This eliminates one of the biggest hurdles (since compressed airheats up significantly when it reaches 100-200 Barr).

FIG. 7 illustrates another example embodiment of an energy storagesystem 20′ which includes fluid circuit 22′ and electrical unit 24′.Electrical unit 24′ is connected through shaft 26′ to operate as a motorin a first phase of operation and to operate as a generator in a secondphase of operation. The energy storage system 20′ further comprises, inaddition to comparably numbered elements understood from previousembodiments, second fluid container 130; second hydraulic motor/pumpunit 134; and, third hydraulic motor/pump unit 135. The second fluidcontainer 130 is situated so that content of second fluid container 130is at a second bladder pressure level P₂, the second flexible bladderpressure level being less than the first pressure level P₁. The secondhydraulic motor/pump unit 134 is operatively connected to the electricalunit 24′ and fluidically connected between the second fluid container130 and third hydraulic motor/pump unit 135. The second hydraulicmotor/pump unit 134 is connected by pipe 150 to third hydraulicmotor/pump unit 135. The third hydraulic motor/pump unit 135 isfluidically connected between the second hydraulic motor/pump unit andfluid container 30′. The second hydraulic motor/pump unit 134 and thethird hydraulic motor/pump unit 135 are configured during the firstphase of operation to operate as pumps to transmit fluid from secondfluid container 130 to fluid container 30′. The second hydraulicmotor/pump unit 134 and third hydraulic motor/pump unit 135 areconfigured during the second phase of operation to operate as motors asfluid from the fluid container 30′ is transmitted to second fluidcontainer 130. The electrical unit 24′ is configured during the firstphase of operation to operate as the motor for the second hydraulicmotor/pump unit 134 and during the second phase of operation to operateas a generator driven by the second hydraulic motor/pump unit 134.

The example embodiment of FIG. 7 thus brings to the surface (e.g., abovereference level P_(R)) the transformer/switch 90′ andmotor-generator-serving electrical unit 24′. This has an advantage ofavoiding the need for pressure chambers or sealants and the like whichare needed around these electrical components when submerged orimmersed.

In the FIG. 7 embodiment, the working fluid in pipe 50 is used as meansfor energy transfer between the surface and the depth, rather than anelectrical cable such as shown in previous embodiments. At the surface,the electrical energy from the grid goes to switch 164 to electricalunit 24′ coupled with the second hydraulic motor/pump unit 134 pumpingthe working fluid from second fluid container 130 to third hydraulicmotor/pump unit 135. The second fluid container 130 can take the form ofa second flexible bladder. The mechanical energy is transferred throughshaft 92 to the hydraulic motor/pump unit (HM/PU) 34 and, as in theprevious embodiment, empties tank 32 into fluid container 30, therebystoring potential energy in the first phase or accumulation phase.

At a time of peak electrical demand, the whole system of FIG. 7 works asa generator, operating essentially in reverse as understood from theforegoing description and embodiments. In particular, hydraulicmotor/pump unit (HM/PU) 34 now reverses its operation to function as anhydraulic motor; third hydraulic motor/pump unit 135 operates as ahydraulic pump to pump working fluid up pipe 50 to second hydraulicmotor/pump unit 134; 134 operates as a motor to drive electrical unit24′ to function as an electrical generator.

The embodiment of FIG. 7 thus employs high-pressure fluid to transferenergy between the cells (bottom of the ocean) and the surface. Thisenables the electrical power equipment (reversible pump-motor,generator, etc.) to function “dry” above water.

FIG. 8 illustrates another example embodiment of an energy storagesystem 20″ which includes fluid circuit 22″ and electrical unit 24″.Electrical unit 24″ is connected to operate as a motor in a first phaseof operation and to operate as a generator in a second phase ofoperation. The energy storage system 20″ further comprises, in additionto comparably numbered elements understood from previous embodiments,second fluid container 130″. Further, in the FIG. 8 embodiment the firsthydraulic motor/pump unit 34″ is fluidically connected between storagecell or tank 32″ and second fluid container 130″ for communicating asecond working fluid between the tank 32″ and the second fluid container130″. In the example embodiment of FIG. 8, the first working fluidcomprises compressed gas which is communicated by hose or pipe 50″between tank 32″ and fluid container 30″. The first fluid container 30″is submerged in a liquid 160 and has a fluid container first internalregion 162 in communication with the submerging liquid 160 and a fluidcontainer second internal region 164 in communication with thecompressed gas. The first hydraulic motor/pump unit 34″ is configuredduring the first phase of operation to operate as a pump to transmit thesecond working fluid from the second fluid container 130″ to the tank32″ and thereby drive the first working fluid from tank 32″ to the firstinternal region 160 of fluid container 30″.

The first hydraulic motor/pump unit 34″ is configured during the secondphase of operation to operate as a motor as the second working fluid isdriven by the first working fluid from the tank 32″ to the second fluidcontainer 130″. In this regard, escape of the first working fluid in theform of compressed gas from fluid container first internal region 162,as controlled by valves or the like in pipe 50″ (or otherwise situatedin fluid circuit 22″) pushes the second working fluid from tank 32″through hydraulic motor/pump unit (HM/PU) 34″ (acting as a motor) intosecond fluid container 130″. The electrical unit 24″ is configuredduring the first phase of operation to operate as the motor for thefirst hydraulic motor/pump unit 34″ and during the second phase ofoperation to operate as a generator driven by the first hydraulicmotor/pump unit 34″.

For energy transport the FIG. 8 embodiment thus does not use anelectrical cable or hydraulic fluid, but compressed fluid as the workingfluid. The compressed fluid (e.g., compressed air) as the first workingfluid is situated at the top of pressure tank 32″ and thus presses downon the second working fluid (e.g., hydraulic fluid) in the same tank. Inan example implementation, the compressed air of the first working fluidcan have a pressure substantially equal to the depth pressure (which isconstant) of the previous embodiments. This advantageously avoidscompressing air from the atmospheric pressure, thereby overcoming adeficiency of other techniques such as CAES, for example.

In the first or accumulation phase of the FIG. 8 embodiment, electricalenergy from the grid goes through the transformer/switch 90″ toelectrical unit 24″ operating as a motor, coupled with hydraulicmotor/pump unit (HM/PU) 34″ operating as a pump. Pressure tank 32 isthus filled with the second working fluid, which pushes the firstworking fluid (e.g., compressed air) downwards through tube 50″ into theopened chamber (e.g., fluid container first internal region 162) offluid container 30″.

In the second or recuperation-generating phase of the FIG. 8 embodiment,the second working fluid (e.g., hydraulic fluid) in tank 32″ is simplyturbined by hydraulic motor/pump unit (HM/PU) 34″ acting as thehydraulic motor and through electrical unit 24″ and transformer/switch90″ back to the grid.

The FIG. 8 embodiment comprises a long pressure pipe 50″ between surfaceand depth, in an example implementation of considerable diameter (e.g.,6-12″), and a surface pressure tank (e.g., tank 32″) with relativelythicker walls.

Systems as described herein can also be use deep in inundated mines. Onthe ocean, the “surface” should be a marine platform. Some embodimentshave the advantage of installing the electrical generator andtransformers (static converters if using direct current) above water. Onthe other hand, extra pressure tanks add to investment and friction onthe downward air tube may decrease the recuperation factor.

Any suitable fluid as be used as the working fluid for communicationbetween tank(s) and the flexible bladder(s). Examples of the workingfluid include but are not limited to hydraulic fluid or hydraulic oil,glycol, or water with any form of lubricant inside.

One or more of the above-described embodiments have numerous advantages,such as (but not limited to): Being scalable; low prototype andproduction price; ability to be situated in multiple locations;consistency with actual energy policy trends; accessibility bysubmarines able to work at such depth; better storing efficiency thanCAES. This storage device is remarkably inexpensive compared withinvestments for CAES or gravitational hydropower storage.

The foregoing embodiments thus provide electricity re-distributiontechniques suited for meeting increasing peak demands.

Although the description above contains many specificities, these shouldnot be construed as limiting the scope of the invention but as merelyproviding illustrations of some of the presently preferred embodimentsof this invention. Thus the scope of this invention should be determinedby the appended claims and their legal equivalents. Therefore, it willbe appreciated that the scope of the present invention fully encompassesother embodiments which may become obvious to those skilled in the art,and that the scope of the present invention is accordingly to be limitedby nothing other than the appended claims, in which reference to anelement in the singular is not intended to mean “one and only one”unless explicitly so stated, but rather “one or more.” All structural,chemical, and functional equivalents to the elements of theabove-described preferred embodiment that are known to those of ordinaryskill in the art are expressly incorporated herein by reference and areintended to be encompassed by the present claims. Moreover, it is notnecessary for a device or method to address each and every problemsought to be solved by the present invention, for it to be encompassedby the present claims. Furthermore, no element, component, or methodstep in the present disclosure is intended to be dedicated to the publicregardless of whether the element, component, or method step isexplicitly recited in the claims. No claim element herein is to beconstrued under the provisions of 35 U.S.C. 112, sixth paragraph, unlessthe element is expressly recited using the phrase “means for.”

1. An energy storage system comprising: a fluid circuit comprising: afirst fluid container situated so content of the first fluid containerexperiences a first pressure level; a tank configured so that content ofthe tank is at a second pressure level, the second pressure level beingless than the first pressure level; a first hydraulic motor/pump unitconnected to communicate a first working fluid between the tank and thefirst fluid container; an electrical unit configured to operate as amotor in a first phase of operation and to operate as a generator in asecond phase of operation, wherein in the first phase of operationelectricity is supplied to the first hydraulic/motor unit whereby thefirst hydraulic/motor unit transmits the first working fluid from thetank into the first fluid container, and wherein in the second phase ofoperation pressurized first working fluid in the first fluid containeris transmitted from the first fluid container through the firsthydraulic/motor unit to the tank thereby causing the electrical unit togenerate electricity.
 2. The apparatus of claim 1, wherein the firsthydraulic motor/pump unit is connected between the tank and the firstfluid container; wherein the first pressure level is vacuum; and whereinthe first fluid container is submerged whereby the first pressure levelis hydrostatic pressure.
 3. The apparatus of claim 2, wherein the firstfluid container comprises a first flexible bladder.
 4. The apparatus ofclaim 2, wherein the fluid circuit and the electrical unit are situatedbelow the reference pressure level.
 5. The apparatus of claim 2, furthercomprising a ballast configured to prevent at least a portion of thesystem from floating.
 6. The apparatus of claim 3, further comprising: asecond fluid container situated so that content of the second fluidcontainer is at a second container pressure level, the second containerpressure level being less than the first pressure level; a secondhydraulic motor/pump unit; a third hydraulic motor/pump unit; whereinthe second hydraulic motor/pump unit is operatively connected to theelectrical unit and fluidically connected between the second fluidcontainer and the third hydraulic motor/pump unit, wherein the thirdhydraulic motor/pump unit is fluidically connected between the secondhydraulic motor/pump unit and the first fluid container; and wherein thesecond hydraulic motor/pump unit and the third hydraulic motor/pump unitare configured during the first phase of operation to operate as pumpsto transmit fluid from the second fluid container to the first fluidcontainer, and during the second phase of operation to operate as motorsas fluid from the first fluid container is transmitted to the secondfluid container; wherein the electrical unit is configured during thefirst phase of operation to operate as the motor for the secondhydraulic motor/pump unit and during the second phase of operation tooperate as a generator driven by the second hydraulic motor/pump unit.7. The apparatus of claim 1, further comprising: a second fluidcontainer, the first hydraulic motor/pump unit being fluidicallyconnected between the tank and the second fluid container forcommunicating a second working fluid between the tank and the secondfluid container; wherein the first working fluid comprises compressedgas; wherein the first fluid container is submerged in a liquid, thefirst fluid container having a fluid container first internal region incommunication with the liquid and a fluid container second internalregion in communication with the compressed gas; wherein the firsthydraulic motor/pump unit is configured during the first phase ofoperation to operate as a pump to transmit the second working fluid fromthe second fluid container to the tank and thereby drive the firstworking fluid from the tank to the fluid container first internal regionand during the second phase of operation to operate as a motor as thesecond working fluid is driven by the first working fluid from the tankto the second fluid container; wherein the electrical unit is configuredduring the first phase of operation to operate as the motor for thefirst hydraulic motor/pump unit and during the second phase of operationto operate as a generator driven by the first hydraulic motor/pump unit.8. The apparatus of claim 1, further comprising: an electrical powersource; a cable network configured during the first phase of operationto convey electricity from the electrical power source to the electricalunit to operate the electrical unit during the first phase of operationand configured during the second phase of operation to transmitelectricity generated by the electrical unit to the electrical powersource.
 9. The apparatus of claim 8, wherein the electrical power sourceis a power grid, a storage cell, or a renewable power source.
 10. Theapparatus of claim 8, further comprising a transformer connected on thecable network between the electrical power source and the electricalunit.
 11. A method of operating an energy storage system, the methodcomprising: situating a first fluid container so content of the firstfluid container experiences a first pressure level; situating a tank sothat content of the tank is at a second pressure level, the secondpressure level being less than the first pressure level; providing anelectrical unit configured to operate as a motor in a first phase ofoperation and to operate as a generator in a second phase of operation;communicating a first working fluid between the tank and the first fluidcontainer in a first direction during the first phase of operation andin a second direction during the second phase of operation, in the firstphase of operation supplying electricity to the first hydraulic/motorunit whereby the first hydraulic/motor unit transmits the first workingfluid from the tank into the first fluid container; in the second phaseof operation transmitting pressurized first working fluid in the firstfluid container from the first fluid container through the firsthydraulic/motor unit to the tank thereby causing the electrical unit togenerate electricity.
 12. The method of claim 11, further comprisingconnecting the first hydraulic motor/pump unit between the tank and thefirst fluid container; situating the first fluid container below areference pressure level; and submerging the first fluid containerwhereby the first pressure level is hydrostatic pressure.
 13. The methodof claim 12, further comprising using a first flexible bladder as thefirst fluid container.
 14. The method of claim 12, further comprisingsituating the fluid circuit and the electrical unit below the referencepressure level.
 15. The method of claim 12, further comprising using aballast to prevent at least a portion of the system from floating. 16.The method of claim 13, further comprising: situating a second fluidcontainer situated so that content of the second fluid container is at asecond container pressure level, the second container pressure levelbeing less than the first pressure level; providing a second hydraulicmotor/pump unit and a third hydraulic motor/pump unit, the secondhydraulic motor/pump unit being operatively connected to the electricalunit and fluidically connected between the second flexible bladder andthe third hydraulic motor/pump unit, wherein the third hydraulicmotor/pump unit is fluidically connected between the second hydraulicmotor/pump unit and the first flexible bladder; during the first phaseof operation operating the second hydraulic motor/pump unit and thethird hydraulic motor/pump unit as pumps to transmit fluid from thesecond flexible bladder to the first flexible bladder, during the secondphase of operation operating the second hydraulic motor/pump unit andthe third hydraulic motor/pump unit as motors as fluid from the firstflexible bladder is transmitted to the second flexible bladder; duringthe first phase of operation operate the electrical unit as the motorfor the second hydraulic motor/pump unit; and during the second phase ofoperation operating the electrical unit as a generator driven by thesecond hydraulic motor/pump unit.
 17. The method of claim 11, furthercomprising: providing a second fluid container with the first hydraulicmotor/pump unit being fluidically connected between the tank and thesecond fluid container for communicating a second working fluid betweenthe tank and the second fluid container; providing the first workingfluid as comprising compressed gas; submerging the first fluid containerin a liquid and providing in the first fluid container a fluid containerfirst internal region in communication with the liquid and a fluidcontainer second internal region in communication with the compressedgas; during the first phase of operation operating the first hydraulicmotor/pump unit as a pump to transmit the second working fluid from thesecond fluid container to the tank and thereby drive the first workingfluid from the tank to the fluid container first internal region; duringthe second phase of operation operating the hydraulic motor/pump unit asa motor as the second working fluid is driven by the first working fluidfrom the tank to the second fluid container; during the first phase ofoperation operating the electrical unit as the motor for the firsthydraulic motor/pump unit; and during the second phase of operationoperating the hydraulic motor/pump unit as a generator driven by thefirst hydraulic motor/pump unit.